1. Field of the Invention
The present invention relates to processors for color video signals, and more specifically to such processors which limit the amplitude of a composite color video signal by limiting the amplitude of color component signals.
2. Related Art
In analog color video signal processing, input red, green and blue color signals (RGB) may be matrixed to color signals and luminance (Y) signals, where the color signals may be in the form of color difference signals, such as R-Y and B-Y. The color difference signals contain the hue and saturation information from the original color video. Luminance, hue and saturation may be processed or corrected using color correction processors, and the luminance, R-Y and B-Y signals rematrixed to RGB, which may then be combined into an encoded NTSC or PAL composite color video signal. While the input color video signal prior to processing typically may not include color signals whose amplitudes are outside predefined limits such as industry standards or regulatory limits set by the Federal Communications Commission (FCC), the signal processing of the luminance, R-Y and B-Y signals may result in an output composite color video signal having amplitudes outside FCC limits or other predefined limits. To eliminate the possibility of such high amplitudes, an analog processing amplifier clips the appropriate signals in the composite video at the desired levels so as not to exceed FCC limits. One such processing amplifier is marketed by Leitch Video of America, Model No. VPA-330N.
With the advent of digital video processing, digital composite color video signals, called D2, can be processed digitally, as can the digital component signals for luminance, R-Y and B-Y, called D1. However, there is no device to limit the amplitudes of the data in the D1 or D2 formats except as may be inherent in the signals being limited to 8 bits of data. 8 bits allows 256 different incremental values from a minimum value at 0 to a maximum value at 255. However, because the industry has selected the maximum pre-defined value to occur at the 236th incremental value and the minimum predefined value to occur at 16, there are at least sixteen possible incremental values the digital signals can take above and below the pre-defined limits. If the signals exceed those limits, the resulting composite video formed from the component signals may exceed the pre-defined limits.
There is a need for a processor for insuring that the D1 signals (digital luminance, R-Y and B-Y) are limited so as to keep the resulting encoded NTSC or PAL composite signals within the pre-defined limits. This should be done in such a way that the composite signal is maintained within the pre-defined limits while still insuring that any processing of the color video signals is carried through with a minimum of change to the luminance, hue or saturation of the resulting composite signal.